<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        *{box-sizing: border-box; padding: 0;margin: 0;}
        body{
            padding: 50px
        }
        .item{
            width: 500px;
            height: 200px;
            margin: 0 auto;
            padding: 15px;
            border:2px solid rgba(63,174,174,1);
            border-radius: 20px;
            position: relative;
        }    
            h3{
                position: absolute;
                top: -15px;
                left: 50%;
                transform: translateX(-50%);
                background: #fff;
                padding: 0 50px;
                z-index: 2;;
            }
             h3:before, h3:after{
                content: '';
                position: absolute;
                top: -7px;
                width: 12px;
                height: 12px;
                border-radius: 6px;
                background-color: rgba(63,174,174,1);
                z-index: 3;
            }
             h3:before{
                left: 135px;
            }
             h3:after{
                right: 135px
            }
        }
    </style>
</head>
<body>
        <div class="item">
                <h3> 这里显示文字</h3>
              </div>
</body>
</html>